The present invention generally relates to metallurgical furnaces and, more particularly, to improvements in the design of elongated, internally-cooled supporting members commonly employed in walking beam and so-called pusher-type furnaces.
Metallurgical furnaces are employed for the continuous transport of ingots, slabs, rods, bars or like metallic workpieces through a heating chamber. The so-called pusher-type furnaces push the workpieces along the elongated rails and heat the workpieces on all sides thereof.
In such furnaces, contact between the workpieces and the rails along which they are pushed results in the formation of strip-shaped undercooled zones or darkened areas in the region of the workpiece surface which contacts the support. It will be appreciated that the rails must be cooled, usually by circulating cooling fluid through interior passages of the rails, so that they will not themselves be deformed at the elevated temperatures of the furnace. These undercooled zones are very undesirable because they adversely affect material characteristics, particularly during subsequent rolling.
In order to eliminate the formation of undercooled zones, so-called "riders" or workpiece-engaging elements constituted of heat-insulating material are mounted over the entire length of the rails. The workpieces are supported on these riders for the purpose of preventing undercooling of those portions of the workpieces which would otherwise be in direct contact with the internally-cooled rails.
However, the prior-art proposals have not proven altogether satisfactory in eliminating the formation of these undercooled zones. Basically, the temperature difference which causes this problem is derived from two sources. Firstly, there is the cooling effect of the fluid flowing through the supporting member which plays a major role during the time when the temperature of the workpieces is relatively constant. Secondly, there is the screening effect which hinders the flow of heat energy caused by the presence and location of the supporting member itself with respect to heat being directed towards the underside of the workpiece. The screening effect has its major impact during the time when the temperature of the workpieces is being increased.
It is known in the prior art to configurate the supporting member as narrow as possible in order to correspondingly reduce the screening effect. However, a very narrow supporting member has little mechanical rigidity and therefore tends to sag along its length. Vertically-arranged supports are generally arranged at selected intervals along the length of the supporting member to hold up the entire rail. If the supporting member sags, then a great number of such vertically-arranged supports will be needed which is especially undesirable since they not only consume heat due to their own internal cooling, but also screen the flow of heat energy towards the underside of the workpiece.
It has been further proposed to configurate the supporting member as a rectangle whose height is greater than its width so as to better withstand the tendency of the elongated supporting member to sag in a downward direction. However, because of the reduced width, the rectangularly-shaped supporting member tends to buckle transversely of its elongation, thereby still resulting in a mechanically unstable structure.
It is still further known to configurate the supporting member as an equilateral triangle, one of whose sides, or base, faces the lower portion of the furnace so that the base is horizontal to the furnace floor. The upwardly-directed apex of the triangularly-shaped supporting member is flattened so as to support a workpiece. Although this proposal is relatively much more mechanically stable as compared with the previously-mentioned prior-art proposals, this proposal is disadvantageous because the base is quite wide and therefore screens heat from reaching the underside of a workpiece. This proposal requires a very wide base in order to resist turning moments from bending and buckling the rail.
Thus, the current state of the art has two conflicting requirements. In order to make the structure sufficiently strong to resist bending, either a great number of vertically-arranged supports or a relatively massive supporting member is needed -- both of which tend to screen heat. On the other hand, in order to uniformly warm all sides of a workpiece, it is desirable to reduce the cross-section of the rail which, of course, causes the rail to buckle and sag.